1. Field of the Invention
The present invention relates to a surge arrester having a gas-filled housing in which, by means of a tubular insulating body, copper electrodes are spaced opposite one another and have a stepped, truncated conical shape, which electrodes, in the region of the active surfaces thereof, are designed with walls thicker than on the conical sides in the region of the connection to the insulating body.
2. Description of the Prior Art
Evacuated tubeless surge arresters having truncated, conically-shaped electrodes are known in the art (German published application No. 1,951,015) which, in the area of the active surfaces, are designed with walls which are thicker than the conical sidewalls in the area of transition to the tubular insulating body. It is also known per se, that the electrodes in the area of the active surfaces can have a flat waffeling for the application of an activating substance. However, one is not apprised from this art as to the nature of the activating substance. The electrodes consist of a Ni-Fe-Co alloy, on the exterior side of which electrical leads are attached.
In addition, surge arresters having evacuated tubes are known, in which the massive electrodes consist of copper, such as in U.S. Pat. No. 3,454,811. In the case of surge arresters of this type, no waffeling is provided for anchoring an activating layer on the active electrode surfaces. A special solution even provides the application of a carbon layer upon the electrodes in order to avoid erosion and the production of cavities upon the active surfaces of the electrodes under discharge conditions of the arrester.
Gas discharge surge arresters should be efficient and long-lived. Therefore, in increasing measures a value is placed, in addition to the alternating and surge current loading capacity, upon higher actuator or switch life-span characteristics. Switch life-span tests are conducted with pulse-shaped surge currents, opposed to the usual surge current tests, for example 10 kA wave 10/50 .mu.s, display lesser current intensities and longer times, for example, 500 A wave 10/1000 .mu.s. The average attainable number of circuits by which the surge arresters do not lose their ability to function, is evaluated, that is, the response DC current and the installation may not change above prescribed values.
The sum of necessary electrical characteristics is primarily determined by the size of the electrodes, the material, the electrode activating substance, the type of gas and the gas pressure. The electrode materials used in known gas discharge surge arresters are predominantly iron-nickel-cobalt alloys, which, in respect of the coefficient of expansion, are accommodated to the ceramic of the insulating body. Copper leads of a component can be reproducibly securely attached to such electrodes. For the protection of signaling lines, surge arresters which are designed as air discharge devices having carbon electrodes 10, because of their slight electrode spacings of approximately 0.05 mm, toward fine connections.